This model is not supported when using X-OpenAI-Internal-Codex-Responses-Lite

What version of the Codex App are you using (From “About Codex” dialog)?

26.623.141536

What subscription do you have?

plus

What platform is your computer?

Microsoft Windows NT 10.0.26200.0 x64

What issue are you seeing?

This model is not supported when using X-OpenAI-Internal-Codex-Responses-Lite.

What steps can reproduce the bug?

Reproduction:

codex exec -m gpt-5.4 --skip-git-repo-check "Reply with exactly: OK"

Result:

OpenAI Codex v0.143.0
model: gpt-5.4
provider: custom
codex
OK

Then:

codex exec -m gpt-5.5 --skip-git-repo-check "Reply with exactly: OK"

Result:

{
"type": "error",
"error": {
"type": "invalid_request_error",
"code": "unsupported_value",
"message": "This model is not supported when using X-OpenAI-Internal-Codex-Responses-Lite.",
"param": "model"
},
"status": 400
}

What is the expected behavior?

GPT-5.5 should work with a ChatGPT subscription account in Codex, or Codex should not route GPT-5.5 through the Responses-Lite transport if that transport does not support it.

Actual behavior:

GPT-5.5 fails with:

This model is not supported when using X-OpenAI-Internal-Codex-Responses-Lite.

while GPT-5.4 works in the same environment.

This looks like a model routing or model metadata issue for GPT-5.5 on the ChatGPT subscription / OpenAI auth path, not a general network or account issue.

Additional information

_No response_